The neem tree, a tropical evergreen, has been used for centuries as a source of pesticides to which insects have not developed a resistance. Various neem seed extracts, particularly the ones containing the hydrophilic, tetranortriterpenoid azadirachtin, are known to influence the feeding behavior, metamorphosis (insect growth regulating [IGR] effect), fecundity, and fitness of numerous insect species belonging to various orders.
It is known that neem oil, containing azadirachtin, may be mechanically pressed from neem seeds in the cold by using oil presses or may be extracted using alcohols or other solvents using Soxhlet apparatus. Small amounts of neem oil can be obtained by kneading neem seed powder by hand after adding some water (Schmutterer & Helip 1988). Thus the term `neem oil` has been used to describe a variety of materials containing a mixture of both hydrophilic and hydrophobic extractables. The variety of extraction methods and resultant variety in composition of neem oil has led to great confusion as to the true properties of "neem oil". Khan and Wassilew (1986) tested the effect of their "neem oil" (prepared by aqueous extraction of neem kernels) on 14 common fungi, including Trichophytonrubrum, T. violaceus, T. concentrichus, T. mentagrophytes, Epidermophyton floccosum, Mierosporum citaneum, Scrophulariopsis brevicaulis, Geotrichum candidum and Fusarium sp and found that it did not inhibit fungal growth and, in fact, the neem oil itself actually contained several species of growing fungi. Yet an anonymous article (Anon. 1986) reported that "10% Neem oil diluted from its emulsifiable concentrate formulation" completely inhibited several species of fungi such as Aspergillus niger, Fusarium moniliforme, Macrophomina phaseolina and Drechslera rostrata. However, the specific details of this formulation were not provided.
Similarly, there are discrepancies in the literature as to the use of neem oil to control insects. Schmutterer and Hallpap (1986) showed that aqueous neem seed extracts are significantly superior to neem oil in repelling leaf mites (Scrobipalpa ergasina), leaf roller (Phycita melogenu) and leaf hopper (Jacobiella facialna). Mansour et al. (1986) report that the pentane extract of neem seeds was much more effective at controlling the spider mite Tetranychus cinnabarinus than were ethanol or methanol extracts, but surprisingly, the pentane extract was less effective at controlling the mite, Phytoseiulus persimilis than were the ethanol or methanol extracts.
Yamasaki et al showed that the tetranortriterpenoid, salannin, can be isolated from crude plant extracts, obtained from Indian neem seeds which are known to be high in salannin content, using hexane. The biological activity of the salannin extract is reported to be feeding deterency and growth inhibition when applied to chewing insects such as beetles and caterpillars.
This invention provides a novel neem oil extract that is substantially free of azadirachtin and yet is effective as both a fungicide and an insecticide, in particular as a foliar fungicide and insecticide.
It has now been discovered that under the process of this invention, a non-polar, hydrophobic-solvent extracted neem oil, substantially free of azadirachtin, possesses the ability to repel insects from plant surfaces, kill insects at various life stages in particular the egg and larval stages, and control the growth of serious fungal pathogens. This dual activity as both an insecticide and a fungicide in the absence of azadirachtin is novel and unique.
The insecticide and fungicidal activities of the hydrophobically extracted neem oil is unique and unexpected in view of the absence of any known active ingredients.